I don't edit CSS very often, and almost every time I need to go and google the CSS box model to check whether padding is inside the border and margin outside, or vice versa. (Just checked again and padding is inside).

Does anyone have a good way of remembering this? A little mnemonic, a good explanation as to why the names are that way round ...

To me, "padding" just sounds more inner than "margin". Perhaps thinking about the printed page would help? Margins are areas on the far outside - generally, you cannot even print to the edge - they are unmarkable. Within those margins, the content could be padded to provide an extra barrier between the content and the margin?

Once you work in CSS enough, it'll become second nature to remember this.

I've just learnt it over time - the box model is fairly simple but the main reason people find it hard is because body doesn't visibly break the model.

Really, if you give body a margin and a background you should see it surrounded by a white strip. However this isn't the case - body's padding is the same as margin. This establishes a few incorrect things about the box model.

I know this is an answer to your question, but more of a tip. Whenever I am dealing with margin and padding, I will add a border around the part you are working with, then from there, it shows me the room I have to work with. When I am all set, I remove the border.

Tim Saunders gave some excellent advice - when I first got started with CSS, I made a point of building a good, fully commented base stylesheet. That stylesheet has changed many times and remains a terrific resource.

However, when I ran into my own box model problems, I started using 'Mo Pi'. As in, "I'm not fat enough, I need to eat mo pi." Strange, but it worked for me. Of course, I put on twenty pounds while learning CSS...;-)

PAdding is a PArt of an element's PAinting: it extends the element's background. It makes sense to think of a pair element+padding as sharing a common background. Padding is analogous to the painting's canvas: the bigger the padding, the bigger the canvas and therefore background. Border (the painting's frame) would go around that pair. And margin will separate paintings on the gallery wall. Thinking about the concept of object background helps glue the pair object+padding together. The usual explanations of what is inside vs outside do not stick to memory: after a while everybody gets back to the original confusion. Remember also that margins are vertically collapsible and padding is not.